1. Field of the Invention
The present invention relates to an optical device including a light source and a light valve (a liquid crystal panel) having a planar shape which is perpendicular to a direction of an optical axis of light emitted from the light source, and the present invention relates to a projection type video display including this optical device.
2. Description of the Related Art
Conventionally, a projection type video display (such as a projector or a projection television set) has been generally known well, the apparatus includes a projection lens for enlarging an image displayed on a light valve such as a liquid crystal panel or a digital micromirror device (DMD) and for projecting the image onto a screen or the like.
In general, efficiency for light utilization of a projection lens is worse in a peripheral portion than in a portion where an optical axis passes through the projection lens (the latter portion will be hereinafter referred to as an optical axis portion). For this reason, there has been a problem that a peripheral portion of an image projected on a screen (a projected image) becomes darker (what we call “the light amount deterioration in peripheral portion”). Accordingly, there have been various methods proposed for equalizing illuminance distribution of an image projected on a screen (a projected image) or the like.
As an example of these methods, there can be a method cited for equalizing illuminance distribution of an image projected on a screen by combining numerous convex lenses and concave lenses to configure a group of projection lenses, thereby enlarging an image projected on a light valve (see Claim 1, Paragraph [0017], FIG. 2, etc. of Japanese Unexamined Patent Publication No. 2000-147377, for example).
Meanwhile, in order to avoid using a peripheral portion of a projection lens having poor efficiency for light utilization, a method of expanding an image circle by use of a projection lens of a large diameter is also conceivable.